Walking aid

ABSTRACT

Walking aid apparatus comprises handle portion and a shaft portion including a ground-contacting ferrule, the shaft portion comprising telescopically-mounted cylindrical spindle and sleeve elements and a spring means acting between seats of said spindle and sleeve elements resiliently to restrain relative axial sliding movement, in which the apparatus includes a sliding friction-reducing means between at least one end of the spring means and the associated seat, whereby the handle portion and the ferrule are axially rotatable to accommodate twisting movement as between the user and the ground in use. The sliding friction-reducing means results in controlled rotation as between the spring means and the spindle and/or elements with considerable benefits to the user in avoiding tortional loading to the twist, elbow and/or shoulder joints which can be especially painful to those who suffer from arthritis.

[0001] This invention relates to walking aids with resiliently-mountedfeet, intended to alleviate problems experienced by users ofconventional walking aids arising from shock loading transferred to themuscles of the hands, wrists, arms and shoulders.

[0002] Physiotherapists have evidence which suggests that the muscles ofthe shoulder in particular and also the muscles of the hands, wrists andarms are stressed when using normal walking aids. Persons who havesustained tears of the muscles of the shoulder tend to experiencedifficulty when using a rigid, uncushioned walking stick, crutch orZimmer-frame. Similarly, persons who have osteo-arthritis or rheumatoidarthritis often experience problems when using rigid support aids. Thosewho have hip and knee arthritis and have rotator cuff regeneration ortears in the shoulder also tend to be uncomfortable with rigid walkingaids.

[0003] In order to alleviate such problems, walking aids withshock-absorbing feet have been proposed. One such device is described inGB-A-2318510, in which the foot member slides telescopically over anupper sleeve, a spring providing for resilience in the sliding movement.Another such device is described in WO 00/10502, in which it is statedto be desirable that the ground-contacting ferrule can rotate axiallywith respect to the shaft, in order to promote user comfort andconvenience. However, it has been found in practice that freedom ofrotation is dependent on the extent to which one or both ends of thespring can rotate with respect to the annular spring-contactingload-bearing area and that, in practice, such rotational movement is notsmooth but on the other hand is subject, under twisting movement exertedby the user on the handle, to intermittent periods of rotational freedomseparated by intervals of sticking, in which static friction and kineticfriction alternate with consequential rotational jarring experienced bythe user.

[0004] In an attempt to overcome this problem, it has been proposed tointroduce ball or roller bearings to enhance the freedom of rotation butit has surprisingly been found that the resulting walking aid ispotentially disadvantageous or even dangerous in that, if placed on theground at an angle to the vertical, the ferrule tends to rotate underpressure, resulting in the lower end of the shaft moving sideways andthe walking aid failing to support the user's weight. It is therefore anobject of the present invention to provide a walking aid with arotatable ground-contacting ferrule which, nevertheless, provides forcontrolled or limited but nevertheless smoothly-operating rotation.

[0005] According to one aspect of the present invention, walking aidapparatus comprises a handle portion and a shaft portion including aground-contacting ferrule, the apparatus comprisingtelescopically-mounted relatively rotatable elements and spring meansacting between said elements resiliently to restrain relativecompression movement, in which the bearing surfaces of the spring meansand at least one element comprise sliding friction-reducing materialswhereby rotation between the handle portion and the ferrule accommodatestwisting movement as between the user and the ground in a controlledmanner.

[0006] By “sliding friction-reducing materials” in this specification ismeant a materials couple which reduces the friction between at least oneend of the spring means and the associated element, relative axialrotation being accommodated by sliding movement therebetween. It hasbeen found that the use of sliding friction-reducing materials resultsin controlled rotation as between the spring means and at least one ofthe telescopic elements with considerable benefits to the user inavoiding tortional loading to the wrist, elbow and/or shoulder jointswhich can be especially painful to those who suffer from arthritis,without the disadvantages arising from uncontrolled rotation such asresults from the use of ball or roller bearings.

[0007] The bearing surface of the at least one element which is capableof axial rotation relative to the spring means may be an integral partof the element itself or alternatively may comprise a separatefriction-reducing element having a spring-contacting surface and anoppositely-facing surface which bears against a seat of said element,rotational sliding movement taking place between the spring means andthe separate element and/or between the separate element and the seat.The sliding friction-reducing element preferably comprises an annularwasher which may be configured as a cup washer, the cup comprising thespring-facing surface and a peripheral wall to encompass the extremityof the spring means. The material from which the slidingfriction-reducing element is formed should preferably be sufficientlyhard to be accurately machined with a substantially flat seat-facingarea while providing for the required degree of friction with the othermaterial of the couple to give controlled rotation under loadconditions. Suitable materials include engineering plastics materialssuch as acetal-type copolymers which may optionally be glass- or fibre-reinforced. However, the choice of material is to some extent governedby the diameter of the ferrule or at least the ground-contacting lowersurface thereof, since a larger-diameter ferrule will have a greaterresistance to twisting movement on the ground and, hence, a materialwith less inherent lubricitiy is preferred for the friction-reducingmeans, in order to provide the desired controlled rotation. Where theseat of the telescopic element bears directly on the spring means,similar criteria as to the choice of materials apply.

[0008] The telescopically-mounted relatively rotatable elementstypically comprise an outer sleeve element and an inner spindle element,the elements being capable both of relative axial sliding movement toaccommodate compression and expansion as a load, is applied to orreleased from the handle portion of the apparatus and of relative axialrotation to accommodate twisting movement as between the user and theground in use.

[0009] The spring means may be any resilient element and may comprisefor example a helical spring, a pneumatically- orhydraulically-controlled strut or a resilient elastomeric material;conventionally, a helical stainless steel spring is used but otherresilient materials or assemblies may equally be used in the inventiveapparatus. The inner or spindle telescopically-mounted element may havean inner co-axial neck portion of reduced diameter, an annular gap beingdefined between the neck portion and the sleeve element and whichaccommodates the spring means which, conveniently, comprise a helicalspring. However, in another arrangement, the innertelescopically-mounted element has an inner end face which bears,directly or via a friction-reducing element, on one end of the springmeans. In such an arrangement, the spring means may comprise a block,typically a cylindrical block, of resilient elastomeric material,although one or more spherical, spheroidal or ellipsoidal blocks may beused, preferably two such blocks of respectively different resilience orselected from blocks of different resilience to vary the force requiredto compress the elements. Thus, for example, spheres may be selectedfrom hard (H) and soft (S) resilient materials and compressibility maybe varied by using H-H, H-S or S-S combinations although preferably atleast one hard element is used to render the extent of controlledrotation to be substantially independent of applied compression forces.In yet another arrangement, the spring means bears directly on theferrule or is integrally formed with the ferrule from a suitableelastomeric material. The spring means is preferably pre-loaded so that,even when in the fully-extended position of the telescopically-mountedelements, the spring means nevertheless remains partially compressed,thereby causing the apparatus to exhibit the controlled rotationproperty under a no-load or very light loading exerted on the apparatusthrough the handle portion.

[0010] Preferably, the apparatus includes cylindrical bushes journalledbetween the cooperating axially-slidable surfaces of thetelescopically-mounted elements, the bushes enhancing the relative axialsliding movement and optionally assisting to a lesser extent in thecontrolled rotation. The bushes are preferably formed from a suitableplastics material which may comprise nylon or an engineering plastics asin the case of the sliding friction-reducing element.

[0011] The use of a pneumatically- or hydraulically-controlled strut,for example a nitrogen-damped cylinder and piston, for the spring meansis advantageous in that the damping force may be adjusted according tothe weight of the, user by pre-loading to a particular desired gaspressure, for example by the physiotherapist. The ability to increase ordecrease the pressure enables stocks of a single unit to be maintained,to be selectively adapted to the requirements of the individual user atthe time of supply.

[0012] In an alternative way of pre-loading the spring means, the distalend of the inner telescopically-mounted element may comprise ascrew-threaded portion carrying a lock nut which bears on the outerelement to adjust its position relative to the inner element, therebycompressing the spring means. The distal end of the outer element mayhave a counter-bore to accommodate the lock nut; the open end or mouthof the counter-bore may accommodate resilient damping means to act as acushion for the distal end of the inner element and lock nut onfull-load compression of the spring means. Additionally, the proximalend of the outer element, which in use accommodates the spring means,may be formed with an annular groove formed in the wall thereof andwhich carries a resilient O-ring, preferably supported on aninner-extending shoulder constituted by one wall of the groove. Wherethe inner element comprises a smaller-diameter neck portion extendingco-axially of the cylindrical portion for carrying the spring means andthe pre-loading lock nut, an annular shoulder is defined between thecylindrical portion and the neck portion and which makes contact withthe O-ring at the position of maximum compression movement while stillretaining the ability for controlled rotation. Desirably, wherecylindrical bushes are contained in such an arrangement, they arejournalled at the proximal end between the cylindrical portion and theinner-facing wall of the sleeve element and at the distal end betweenthe plain part of the neck portion and a smaller-diameter portion of thesleeve element.

[0013] The sub-assembly comprising the telescopically-mounted elementsand spring means may be carried, in walking aid apparatus according tothe invention, either towards the ferrule end or towards the handleportion end, or indeed at any intermediate location. It has been foundin practice, particularly for use by people who are relatively infirm,that provision of the sub-assembly close to the handle portion gives agreater sense of control and hence a greater sense of security.

[0014] The shaft portion of waling aid apparatus according to theinvention may comprise an aluminium tube, as in many walking sticks orZimmler-frames used by people under medical supervision, but may equallybe a conventional solid, for example wooden, shaft, since the inventionprovides benefits to walking aids such a conventional walking stickswhere there is no particular medical condition which requires the usethereof. When used with a metal tubular walking aid, the inner elementmay be mounted in the tube, whether at the top or bottom thereof, bymeans of an arrangement as described in WO 00/01502 and comprising gripmeans for inhibiting or preventing removal from the shaft once attachedthereto. Particularly when attached to the upper end of the shaft, boththe inner and outer elements may be carried respectively in acylindrical tube attached to the handle and to the cylindrical shaftusing a grip means such as described in WO 00/01502. Plastics materialsmay also be used for the shaft and/or for one or all of the componentsof the telescopically-mounted sub-assembly, provided that the requireddegree of controlled rotational ability is exhibited as a function ofthe frictional forces between the rotational bearing surfaces.

[0015] In order to avoid any possibility of a pinching movement asbetween the outer telescopically-mounted element and the shaft or handleportions in a position at or approaching maximum compression thereof atleast one of the facing edges of the outer element and the shaft orhandle portions, preferably both, may be provided with a chamfer sothat, even when fully compressed, there remains an annular V-shaped gapbetween the outer walls thereof.

[0016] Embodiments of the invention will now be described by way ofexample with reference to the accompanying drawings of which:

[0017]FIG. 1 shows the general assembly of apparatus according to theinvention for fitting to the upper or lower section of a walking aid andcontaining a helical spring;

[0018]FIG. 2 shows the assembly of FIG. 1 attached to the lower end of awalking aid the shaft of which has a hollow metal tube;

[0019]FIG. 3 shows the assembly attached to the lower end of aconventional wooden walking stick;

[0020]FIG. 4 shows the assembly as attached to the upper end of awalking aid having a hollow metal shaft;

[0021]FIG. 5 shows an embodiment with a compressible rubber spring;

[0022]FIG. 6 shows another embodiment;

[0023]FIG. 7 shows an embodiment with compressible elastomeric spheres,and

[0024]FIG. 8 shows another embodiment with elastomeric spheres.

[0025] Referring firstly to FIG. 1, a lower part 11 of the hollow shaftof a walking aid is attached to an upper part 12 of the shaft via atelescopically-mounted spindle element 13 and a sleeve element 14. Thesleeve element is carried in the upper end of the shaft 11 and is heldtherein by rubber O-rings 15, 16 carried in annular grooves, the groovewhich accommodates O-ring 16 having a lower chamfered wall 17, wherebythe ring 16 is forced into jamming engagement with the inner wall of theshaft 11 on any attempted withdrawal of the sleeve element 14 from theshaft, thereby preventing such withdrawal. The spindle element 13, aboutwhich the sleeve element can rotate, consists of a spindle body 18, aneck 19 and a base 20, the base being similarly inserted in the lowerend of the shaft 12 and retained therein by O-rings 21, 22 carried inannular grooves, the lower groove which accommodates ring 22 having anupper chamfered wall 23. The upper end of the shaft 11 is formed with asloping edge 11 a and, similarly, the lower-facing edge of the base 20of the spindle element is formed as a sloping shoulder 20 a.

[0026] The spindle element is journalled for axial sliding movement inthe sleeve element by means of annular bushes 24, 25 and a helicalspring 26 extends between an upper shoulder formed between the body 18and neck 19 of the spindle element and an inner shoulder at the lowerend of the sleeve element. An O-ring 27 is carried in an inner-facingintermediate annular groove in the sleeve element and serves as aresilient buffer for contact with the upper shoulder on maximumdepression of the spindle element within the sleeve element.

[0027] At each end of the spring 26 and journalled respectively betweenthe machined ends of the coils thereof and the upper and lower shouldersare sliding friction reducing clutch washers 28, 29 formed from anacetal copolymer. The spindle element 13 is retained within the sleeveelement 14 by a Nyloc nut 30 applied to the lower screw threaded end ofthe neck 19 and bearing against the lower annular surface of the sleeveelement via a nylon washer 31 and a rubber washer 32.

[0028] In the position shown in FIG. 1 with the spindle element at itsposition of maximum extension within the sleeve element, the spring 26still exerts pressure as between the respective elements through theclutch washers 28, 29. The clutch washers enable smooth relative axialrotation as between the respective elements and, therefore, between theshaft parts 11, 12, avoiding on the one hand intermittent grip andrelease which would otherwise occur from direct metal-to-metal contactbetween the ends of the spring and the respective shoulders while, onthe other hand, preventing uncontrolled or excess rotation. A similareffect is achieved when compression pressure is applied by a user sothat the spindle element slides within the sleeve element against thepressure exerted by spring 26 until, at the position of maximumcompression, the upper shoulder is in contact with O-ring 27. At thisposition, the sloping ends 11 a, 20 a of the shaft 11 and base 20 of thespindle element 12 are in abutting relationship, the sloping surfacespreventing any possibility of the user's skin or clothing being pinchedbetween the ends of the shafts.

[0029] With reference to FIG. 2, an arrangement similar to thatdescribed with reference to FIG. 1 is shown but the sleeve element 33constitutes the lower end of the shaft of the walking aid and carries arubber ferrule 34. Resilient disks 35 are carried at the lower end ofthe sleeve element 33, to act as a bump-stop for the end of the neckportion 19 of the spindle element.

[0030]FIG. 3 shows an arrangement similar to that described withreference to FIG. 2 but the upper end of the spindle element is formedas a hollow, blind-ended cylinder 36 which receives the lower end of asolid shaft 37 of a walking aid.

[0031]FIG. 4 illustrates a further embodiment in which the spindleelement/sleeve element assembly is carried at the upper end of a walkingstick shaft 38, immediately beneath the handle 39. The upper end of thespindle element is secured, in a manner similar to that described withreference to FIG. 1, in the lower end of a short piece of tubing 40, theupper end of which carries a splined element 41 secured within a cavityformed within the handle 39.

[0032] In the embodiment illustrated, hollow shafts are formed fromaluminium and solid shafts are formed from wood; the respective spindleand sleeve elements are formed from aluminium, although the sleeveelement may be made from stainless steel. In a further embodiment, thearrangement as described with reference to FIG. 2 could be inverted sothat the ferrule is attached to the enlarged body part of the spindleelement and the sleeve element is held within the lower part of theshaft of the walking aid with the lock nut facing upwardly in the shaft.

[0033] As shown in the embodiments illustrated in FIGS. 1 to 4, the baseof the spindle element is preferably adapted to receive a connector parteither for fitting within the shaft of a walking aid or around the lowerend thereof, or to which a ferrule may be directly attached. Asillustrated, the base of the spindle element is formed with an axialcavity to receive the spigot or stub end of the connector part, althoughthe connector part could equally include a cavity to receive a spigot orstub end of the spindle element.

[0034] With reference to FIG. 5, a sub-assembly suitable for fitting tothe upper or lower end of a walking stick shaft consists essentially ofa cylindrical sleeve 51, a piston or plunger body 52 for fitting withinthe sleeve and a resilient cylindrical rubber block 53 carried withinthe cavity of the sleeve. Once assembled, the plunger body is heldcaptive within the sleeve by co-operating inner and outer annularshoulders 54, 55; an O-ring 56 is provided in a groove below shoulder 55to act as a resilient buffer under maximum extension of the plunger withrespect to the sleeve. The lower end of the rubber block 53 bearsagainst the upper end surface 57 of the plunger body and the upper endof the block bears against and is retained by a disc 58 screw-threadedlyengaged in the upper end of the sleeve 51.

[0035] A ferrule (not shown) may be attached to the foot 59 of theplunger which, as shown, is screw-threadedly attached thereto afterinsertion from above of the plunger body. The sleeve and plunger may beformed from a plastics material such as polypropylene or polybutylene.The foot of the plunger may of course be attached to the plunger body bymeans other than screwing, such as by the use of a glue or a solvent forplastics materials, thus welding them together.

[0036] In use, the plunger body is axially rotatable within the sleevebut is restrained from uncontrolled rotation by frictional forcesbetween the mating surfaces of the rubber block 53 and the plunger body.

[0037] Referring to FIG. 6, another embodiment of a sub-assembly fittedto the lower end of a tubular shaft 60 consists of an adapter 61 fittedwithin the lower end of the shaft end a piston or plunger 62 securedwithin and extending axially from the adapter. The plunger 62 slideswithin a cylindrical sleeve 63 and is held captive therein bycooperating inner and outer annular shoulders 64, 65 via O-ring 66. Aclutch washer 67 is provided at the lower end of the plunger formounting one end of a spring 68, the other end being retained by plug 69retained at the bottom of the sleeve 63. A ferrule 70 is carried at thelower end of the sleeve 63. The spring may be a helical spring locatedbetween respective spigots 67 a, 69 a; in an alternative arrangement,the clutch washer can be formed without the spigot 66 a or omittedaltogether, the spigot 69 a can be omitted and the spring could be aresilient cylindrical rubber material or, in yet a further alternativearrangement, the spring in the form of a resilient rubber material couldbe integrally formed with the ground-contacting ferrule, as an insertneck thereof in the lower end of the sleeve 63 and bearing on clutchplate 67 or directly on the lower face of the plunger 62.

[0038] Referring to FIG. 7, a further embodiment using elastomericspheres is shown, in which the components are moulded fromfibre-reinforced nylon such as nylon 66. The sub-assembly is secured tothe lower end of a standard aluminium shaft 70 via a moulded socket 71to which a depending plunger 72 is screw-threadedly attached. Theplunger is slidingly journalled in base sleeve member 73 via acylindrical bush 74 and bears on the upper of two elastomeric rubberspheres 75, the lower of which is carried in an optional shallowdepression formed in the upper surface of a plug 76 which is carried inthe lower end of the sleeve member and to which a ferrule (not shown) isattached. Optionally, the contact surface of the plunger 72 is formedwith a slight concavity or depression to correspond with or provide acurved receiving surface for the upper sphere. The position of maximumextension of the plunger 72 within the sleeve member 73 is determined bythe radially-extended flange 77 of the plunger contacting the lower edge78 the bush 74, itself retained within the upper part of the base sleevemember 73 by engagement between the upper end of the bush 74 and aninner flange 79 of the sleeve member 73. The upper of the two spheres 75is formed from a denser, that is, less resilient, elastomeric materialthan the lower sphere. The sub-assembly is shown under slight axialcompression loading.

[0039] The contacting surfaces of the upper of the elastomeric spheres75 and the plunger 72 provide for controlled axial rotation, theresistance of which is substantially independent of the compressionloading on the spheres, while the lower sphere, compressing more thanthe upper sphere with increasing compression forces increases thecontact area between the lower sphere and the surface of the depressionwith increasing compression loading and resists rotation. The plug 76has a flange 80 which limits the extent to which the plug can be screwedinto the lower end of the sleeve member 73.

[0040] With reference to FIG. 8, the sub-assembly is similar to thatdescribed with reference to FIG. 7 in the use of elastomeric spheres butthe base sleeve member 81 is formed from aluminium tubing,screw-threaded end regions 82 and 83 being provided for attachment of aninner sleeve 84, in which the plunger 85 is journalled, and the lowerplug 86, respectively. In this embodiment, the tubing is of 19 mmdiameter, although tubing of larger diameter, say 22 mm, mayalternatively be used. The plug 86 is unflanged and may thus be screwedas far as necessary within the lower end of the sleeve member to adjustthe axial dimension of the chamber for housing the spheres and, hence,the unloaded pressure (if any) on the spheres.

1. Walking aid apparatus comprising a handle portion and a shaft portionincluding a ground-contacting ferrule, the handle and shaft portionscomprising telescopically-mounted relatively rotatable elements forproviding relative axial movement and including spring means actingbetween said elements resiliently to restrain relative compressionmovement the apparatus comprising means acting between said handle andshaft portions to allow relative axial rotation, characterised in thatthe rotation means comprise sliding friction-reducing materials, wherebyrotation between the handle portion and the ferrule accommodatestwisting movement as between the user and the ground in a controlledmanner, and in that the bearing surface of at least one said element isin direct rotationally-slidable contact with the spring means. 2.Apparatus according to claim 1, in which at least one relativelyrotatable element includes a friction-reducing element inrotationally-slidable contact with the spring means.
 3. Apparatusaccording to claim 2, in which the friction-reducing element comprisesan annular washer.
 4. Apparatus according to claim 3, in which thewasher is configured as a cup washer, the cup comprising thespring-facing surface and a peripheral wall to encompass the extremityof the sprig means.
 5. Apparatus according to any of clams 2 to 4, inwhich the friction-reducing element is formed from an engineeringplastics material.
 6. Apparatus according to any preceding claim, inwhich the spring means comprises a helical spring, a pneumatically- orhydraulically-controlled strut or a resilient elastomeric material. 7.Apparatus according to claim 6, in which the spring means comprises oneor more spheroidal elastomeric elements.
 8. Apparatus according to anypreceding claim, in which the sprig means is attached directly to or isintegrally formed with the ferrule.
 9. Apparatus according to anypreceding claim, in which the spring means is pre-loaded so that when inthe fully-extended position of the telescopically-mounted element, thesprig means is partially compressed.
 10. Apparatus according to anypreceding claim the apparatus including cylindrical bushes journalledbetween the telescopically-mounted elements.
 11. Apparatus according toany preceding claim, in which the inner telescopically-mounted elementhas as inner co-axial neck portion of reduced diameter, an annular gapbeing defined between the neck portion and the outer element, the gapaccommodating the spring means.
 12. Apparatus according to any precedingclaim which the inner-telescopically-mounted element has an inner endface which bears on one end of the means.
 13. Apparatus according to anypreceding claim, in which the telescopically-mounted elements and springmeans comprise a sub-assembly which is carried either toward the ferruleend or towards the handle portion end of the apparatus.
 14. Apparatusaccording to any preceding claim, in which the shaft portion comprises atube and the inner or the outer telescopically-mounted element ismounted in the tube by a grip arrangement comprising an O-ring carriedin an annular groove formed in the element and having a chamfered wall,whereby the ring is forced into jamming engagement with the inner wallof the shaft on any attempted withdrawal of the element from the shaft.15. Apparatus according to any preceding claim in which at least one ofthe facing edges of the outer element and the shaft or handle portionsis provided with a chamfer.
 16. Apparatus according to any precedingclaim in which one of the telescopically-mounted elements is adapted forengagement with a connector part for engagement either within the endportion of a hollow walking aid shaft or around the end portion of asolid walking aid shaft, or to which a ferrule may be attached.
 17. Asub-assembly for attachment to walking aid apparatus aid comprisingtelescopically-mounted relatively axially rotatable elements and springmeans acing between of said elements to r relative compassion movementin which at least one element comprises a sliding friction-reducingmaterial in direct rotationally-slidable contact with the spring means.18. A subassembly according to claim 17, in which one of thetelescopically-mounted elements is adapted for engagement with aconnector part for engagement either within the end portion a hollowwalking aid shaft or around the end portion of a solid walking aidshaft.
 19. In combination, telescopically-mounted relatively rotatableelements and spring means acting between seats of said elementsresiliently to restrain relative compression movement, in which thebearing surfaces of the spring means and at least one seat comprisesliding friction-reducing materials in direct rotationally-slidablecontact, the connector part being adapted for engagement either withinthe end portion of a hollow walking aid shaft or around the end portionof a solid walking aid shaft, the combination being for use with walkingaid apparatus according to any of claims 1 to 18 or a sub-assemblyaccording to any of claim 17 or claim
 18. 20. A sub-assembly accordingto claim 17 or claim 18 or a combination according to claim 19, furtherincluding a ground-contacting ferrule attached to the connector part.21. A sub-assembly according to any of claims 17, 18 or 20 or acombination according to claim 19, in which at least one of saidtelescopically-mounted elements is formed with an outer annular groovehating a chamfered wall for accommodating an O-ring, whereby the elementcan be grippingly mounted within a tube.